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<concept id="GUID-BDDDF68F-F7C3-43AF-8B6C-C77C701FD2A9" xml:lang="en"><title>Framework
requirements for GUI applications</title><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>Applications developed for the Symbian platform can use a number of
different architecture solutions to meet their requirements. One example of
a common approach includes the Model - View - Controller (MVC) pattern used
in GUI-based applications. In this approach, the application is split into
three separate logical parts. Each part contains a different aspect of the
entire application, and has a specific role.</p>
<fig id="GUID-5E3A844B-CCF3-4F2A-82A9-DA7A5B65A572"><title>Logical dependencies in the MVC pattern</title><image href="GUID-A5E152B2-F15C-4809-A52A-BCDDBCD93255_d0e36431_href.png"/></fig>
<p>In this approach, the model:</p>
<ul>
<li><p>contains and manipulates the data in the application</p>
</li>
<li><p>is owned by the controller</p></li>
<li><p>is typically implemented in its own class or classes</p>
</li>
</ul>
<p>the <xref href="GUID-DAC32BB9-C0EB-42FF-A596-C2F1A90A4BD7.dita">view</xref> :</p>
<ul>
<li><p>displays the application state known by the model</p>
</li>
<li><p>receives user input</p></li>
<li><p>notifies the controller of relevant events</p></li>
<li><p>is implemented either with a <parmname>CCoeControl</parmname> derived
class or a <parmname>CAknView</parmname> derived class.</p><p>For more
information on these options, see <xref href="GUID-B5DE1C86-2B16-4B22-887F-7079E54A8ED6.dita">Traditional
Symbian UI application architecture</xref> and <xref href="GUID-68B999C2-0993-4804-9624-42C3D88BE5C7.dita">View
architecture</xref>.</p></li>
</ul>
<p>the <xref href="GUID-FD2CDEB8-0784-4BE5-A775-170F57D71BBC.dita">controller</xref> :</p>
<ul>
<li><p>handles application-wide events</p></li>
<li><p>commands the model, typically based on user input</p>
</li>
<li><p>selects the view to be displayed</p></li>
<li><p>is implemented either with a <xref href="GUID-77329067-34D9-3698-B764-294535E660EB.dita"><apiname>CAknAppUi</apiname></xref>-derived
class or a <xref href="GUID-2DBA2DA9-3DA7-381C-842C-9F6FEEDF973E.dita"><apiname>CAknViewAppUi</apiname></xref> derived class.</p><p>For
more information on these options, see <xref href="GUID-B5DE1C86-2B16-4B22-887F-7079E54A8ED6.dita">Traditional
Symbian UI application architecture</xref> and <xref href="GUID-68B999C2-0993-4804-9624-42C3D88BE5C7.dita">View
architecture</xref>.</p></li>
<li><p>requires the implementation of <xref href="GUID-4F825D83-47A4-36C9-9A25-943A6D799F84.dita"><apiname>CAknApplication</apiname></xref> and <xref href="GUID-935C59EE-AD66-33FE-987B-BD97F5147CC1.dita"><apiname>CAknDocument</apiname></xref> derived
classes.</p></li>
</ul>
<p>The pattern is implemented with the following classes.</p>
<fig id="GUID-B4508A88-B688-4BB7-B42A-31BFF41CD4FA"><title>Relationship between the classes that make up a typical Symbian application</title><image href="GUID-36BB14BD-34B3-4F5D-A670-707710E57585_d0e36549_href.png"/></fig>
<p>The <xref href="GUID-4F825D83-47A4-36C9-9A25-943A6D799F84.dita"><apiname>CAknApplication</apiname></xref>-derived class:</p>
<ul>
<li><p>provides the application object expected by the application
framework when the application is launched.</p></li>
<li><p>defines the application properties.</p></li>
<li><p>creates the <xref href="GUID-935C59EE-AD66-33FE-987B-BD97F5147CC1.dita"><apiname>CAknDocument</apiname></xref> derived class
if it does not exist yet.</p></li>
<li><p>if an instance of the application is already running, switches
to that instance and exits.</p></li>
</ul>
<p>The <xref href="GUID-935C59EE-AD66-33FE-987B-BD97F5147CC1.dita"><apiname>CAknDocument</apiname></xref>-derived class:</p>
<ul>
<li><p>creates the controller class</p></li>
<li><p>is the base class for application documents</p></li>
</ul>
</conbody></concept>